This invention relates to a method for the chemical removal of phosphorus ions from waste water. It particularly relates to a method wherein both simple and condensed phosphates present in waste water are reacted with a trivalent rare earth ion to form an insoluble rare earth phosphate.
The usefulness to mankind of many lakes, rivers and bays in and near population centers is being destroyed because of the influx into these bodies of water of untreated or incompletely treated municipal, industrial and agricultural waste waters containing simple and condensed phosphate salts. These salts cause drastic changes in the biological make-up of these waters. The finding of inexpensive, reliable and efficient ways to remove phosphorus from waste water is essential to restore and maintain these natural water resources.
Many chemical, biological, and combined chemical-biological methods have been used or suggested for removal of phosphates from waste water. The chemical precipitation of phosphate has been widely investigated using calcium, iron, and aluminum salts. Considerable success has been reported, particularly with the use of aluminum and iron salts in a tertiary processing stage in the treatment of waste waters. However, while these methods have been successfully used and have advantageous features, they suffer from several disadvantages. Considerable excess of chemicals is usually required for efficient removal of dissolved phosphate. Generally, careful pH control to avoid both complexing effects and hydroxide precipitation is also required. In addition, the usual processes for regenerating the precipitant, which are generally required because of economic considerations, are complicated and relatively inefficient.